1. Field of the Invention
The present invention relates to a flare-measuring method for measuring flare information of a projection optical system, a flare-measuring mask usable to carry out the flare-measuring method, a mask pattern-correcting method using the flare-measuring method, and an exposure method using the flare-measuring method.
2. Description of the Related Art
In an exposure apparatus which is used in the photolithography step of producing various devices (electronic devices) including semiconductor devices, etc., if a scattered light, which is generated due to the surface roughness of an optical member constructing a projection optical system, forms any flare as a blur of an image around the image to be imaged by the genuine light flux, then the contrast of the image is lowered, and the imaging characteristic is affected thereby. Accordingly, the flare of the projection optical system is measured beforehand; and for example, a shape of a pattern of a reticle (mask) is corrected depending on a result of the measurement to form a target pattern on a wafer (or a glass plate or the like) as the exposure objective. In the case of an exposure apparatus (EUV exposure apparatus) which uses, as the exposure light (exposure light beam), an extreme ultraviolet light or extreme ultraviolet light beam (hereinafter referred to as “EUV light”) having a wavelength of not more than about 100 nm, almost all of optical members including the reticle are reflecting members, wherein the flare tends to appear with ease, while the required resolution is heightened. Therefore, it is necessary to measure the flare highly accurately.
The Kirk method is known as a conventional flare-measuring method, wherein an image of an evaluating pattern, which includes, for example, an annular or zonal transmitting portion (or reflecting portion), is subjected to the exposure via a projection optical system, and the flare is evaluated based on the ratio of an exposure amount provided when an image of the transmitting portion is subjected to the exposure with respect to an exposure amount provided when a center of an image of a light shielding portion disposed inside the transmitting portion is subjected to the exposure (see, for example, Japanese Patent Application Laid-open No. 2007-234716). Recently, in order to further evaluate the flare in each of distinct directions, a flare-measuring method has been also suggested, wherein pairs of bar-shaped patterns are arranged while being directed or oriented in four different directions, and the flare amount is determined for an image of a central gap portion of each of the pairs of bar-shaped patterns directed in one of the different directions (see, for example, Japanese Patent Application Laid-open No. 2008-288338).
According to the conventional flare-measuring method in which the pairs of bar-shaped patterns are arranged while being directed or oriented in the different directions, it is possible to compare the differences (anisotropies) in the distinct directions of the flares. However, even if a large number of the pairs of bar-shaped patterns are arranged while being directed in the different directions, a problem arises such that an area, at which no bar-shaped pattern is arranged, is increased at positions away or separated farther from the measuring point on the image plane, and it is difficult to evaluate the contribution of the flare in relation to all directions.